1. Field of the Invention
The present invention relates to a transflective liquid crystal display device, and more particularly, to a transflective liquid crystal display device having various cell gaps.
2. Description of the Related Art
Liquid crystal display (LCD) devices are widely used as displays in devices such as a portable televisions and notebook computers. Liquid crystal display devices are classified into two types. One is a transmissive type liquid crystal display device using a backlight as a light source, and another is the reflective type liquid crystal display device using an external light source, such as sunlight or an indoor lamp. It is difficult to decrease the weight, the volume, and the power consumption of the transmissive type LCD due to the power requirements of the backlight component. The reflective type LCD has the advantage of not requiring a backlight component, but it cannot operate without an external light source.
In order to overcome the drawbacks of these two types of LCDs, a transflective LCD device which can operate both as a reflective and transmissive type LCD is disclosed. The transflective LCD device has a reflective electrode on a pixel region, wherein the reflective electrode has a transmissive portion. Thus, the transflective LCD device has lower power consumption than the conventional transmissive type LCD device because a backlight component is not used when there is a bright ambient light. Further, in comparison with the reflective type LCD device, the transflective LCD device has the advantage of operating as a transmissive type LCD device using backlight when no bright ambient light is available.
FIG. 1 is an explored perspective view illustrating a typical transflective LCD device. The transflective LCD device includes upper and lower substrates 10 and 20 that oppose each other, and a liquid crystal layer 50 is interposed therebetween. The upper substrate 10 is called a color filter substrate and the lower substrate 20 is called an array substrate. In the upper substrate 10, on a surface opposing the lower substrate 20, a black matrix 12 and a color filter layer 14 including a plurality of red (R), green (G) and blue (B) color filters are formed. That is, the black matrix 12 surrounds each color filter, in the shape of an array matrix. Further on the upper substrate 10, a common electrode 16 is formed to cover the color filter layer 14 and the black matrix 12.
In the lower substrate 20, on a surface opposing the upper substrate 20, a TFT “T” as a switching device is formed in shape of an array matrix corresponding to the color filter layer 14. In addition, a plurality of crossing gate and data lines 26 and 28 are positioned such that each TFT is located near the intersection of the gate and data lines 26 and 28. Further on the lower substrate, a plurality of pixel regions (P) are defined by the gate and data lines 26 and 28. Each pixel region P includes a reflective electrode 22 (reflective portion) and a transparent electrode 24 (transmissive portion). The reflective electrode 22 is made of a metal having a high reflectivity, and the transparent electrode 24 is made of a transparent conductive material, such as ITO (indium tin oxide) or IZO (indium zinc oxide).
FIG. 2, a sectional view of a traditional transflective LCD device, helps to illustrate the operation of such devices. As shown in FIG. 2, the conventional transflective LCD device includes a lower substrate 200, an upper substrate 260 and an interposed liquid crystal layer 230. The upper substrate 260 has a common electrode 240 and a color filter 250 thereon. The lower substrate 200 has an insulating layer 210 and a reflective electrode 220 thereon, wherein the reflective electrode 220 has an opaque portion 222 and a transparent portion 224. The opaque portion 222 of the reflective electrode 220 can be an aluminum layer, and the transparent portion 224 of the reflective electrode 220 can bean ITO (indium tin oxide) layer. The opaque portion 222 reflects the ambient light 270, while the transparent portion 224 transmits light 280 from the backlight device (not shown). The liquid crystal layer 230 includes a plurality of spherical spacers 235 used to keep a fixed layer thickness or cell gap of the liquid crystal layer 230. Thus, the transflective LCD device is operable in both reflective and transmissive modes.
The traditional transflective LCD device, however, has the problem of different color reproduction levels (color purity) in reflective and transmissive modes, due to, referring to FIG. 2, the backlight 280 penetrating the transparent portion 224 passing through the color filter 250 once and the ambient light 270 reflected from the opaque portion 222 passing through the color filter 250 twice. This greatly degrades the display quality of transflective LCDs.
U.S. Publication No. 2002/0003596A1 discloses a method of forming color filters having various thicknesses on the upper substrate, for solving the color purity issue. However, this conventional method requires additional fabrication steps to produce the color filters. Also, it is difficult to align the color filters with the lower substrate.